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100                               STONESFIELD   MAMMALS                            CHAP
A'rnpfiilestes has teeth of the same pattern but has more o
them, the preinolars and molars being respectively four and five
All these animals had the lower jaw inflected. Whether the}
are all Marsupials or not, it is clear that jPhascolotherium anc
jimphilestes should be united and placed away from Amphitheriun
on account of the more primitive forrri of their teeth.
We next come to the Trituberculata.
Among the most celebrated of these remains are a few jaws
discovered in the Stonesfield slates near Oxford, and examined bj
Buckland, Cuvier, and some of the most eminent naturalists of the
beginning of the last century. These jaws have been lately sub-
mitted to a careful re-examination by Mr. Goodrich,1 who hag
increased our knowledge of the subject by exposing from the
rocky matrix in which the jaws lie fresh details of their structure;
it is probable therefore that now all that there is to be learnt
from these specimens has been recorded.
^imphitherium prevostii was a creature about the size of a Bat.
Its jaw was first brought to Dean Buckland about the year 1814,
and described six years later. Buckland thought the jaw to be
that of an Opossum, an opinion in which Cuvier concurred. The
jaw, however, is marked by a groove running along its length, and
this groove was regarded by de Blainville as evidence of the com-
position of the jaw out of more than one element, which would
naturally lead to its being regarded as the jaw of a reptile.2 This
species and another named after Sir Eichard Owen have a dental
formula which, Hke that of the Marsupials, is large as compared with
that of the Placental mammals ; it runs : I 4, C 1, Pm 5, M 6i,e.
64 teeth altogether. This is a larger number than we find in any
existing Marsupial. But as in Marsupials, and in certain Insectivora
also, the angle of the jaw is inflected. These teeth are of the
tritubercular pattern with a " heel." They are in fact closely like
those of the living Myrmecobius ; but not, it should be remarked,
unlike those of certain Insectivora.
Tlie Mammals of the Cretaceous Period.At on time
there was a totally inexplicable gap between the Jurassic and
the "basal Eocene, a series of strata which occupy an enormous
expanse of time in the history of the earth having appeared to
1  "On the Fossil Mammalia from the Stonesfield Slate," Quart. Jown. Micr.
Sci, xxxr. 1894, p. 407.
2  This groove has been, found In the existing Myrmecofava, see p. 154.